Ketchikan is on an island and has no road connection to the rest of Alaska or the contiguous United States. You arrive by air or by sea.
By air: Ketchikan International Airport (KTN) sits on Gravina Island, across the Tongass Narrows from downtown. Alaska Airlines operates daily jet service from Seattle, with connections to other Alaskan cities. A short ferry connects the airport to downtown — the crossing takes about five minutes and runs continuously. The airport ferry is free.
By ferry: The Alaska Marine Highway System connects Ketchikan to Bellingham, Washington (the southern terminus, about 38 hours south) and to Wrangell, Petersburg, Sitka, Juneau, and points north. The ferry is a genuine travel experience: you share the boat with Alaskans going about their lives, not just tourists. Cabins are available; many budget travellers bring a tent and sleep on the deck solarium, which has overhead heating. The scenery through the Inside Passage — fjords, islands, occasional whales — is exceptional.
By cruise ship: Several cruise lines include Ketchikan as a port of call on Alaska itineraries. Ships dock at the downtown waterfront, and the city is easily walkable from the pier. Be aware that multiple ships can arrive simultaneously, turning the small downtown briefly chaotic.
No road connection: There are no roads connecting Ketchikan to the outside world. The Gravina Island Bridge — proposed to connect the airport island and ultimately to a highway — was famously cancelled after national controversy over its cost and was dubbed the "Bridge to Nowhere."